PCAT Biology 3

Question 1

Which enzyme unwinds the DNA double helix ahead of the replication fork?

Accepted Answer

Helicase

Answer

Helicase breaks hydrogen bonds between base pairs and unwinds the double helix, creating the replication fork for DNA synthesis.

Question 2

The Hardy-Weinberg equilibrium requires which of the following conditions?

Accepted Answer

Random mating within the population

Answer

Hardy-Weinberg equilibrium requires random mating, no selection, no mutation, no genetic drift, and no gene flow.

Question 3

Which molecule acts as the final electron acceptor in aerobic cellular respiration?

Accepted Answer

Oxygen

Answer

Oxygen is the terminal electron acceptor in the electron transport chain, combining with electrons and H⁺ to form water.

Question 4

Nondisjunction during meiosis I results in which outcome?

Accepted Answer

All daughter cells receive abnormal chromosome numbers

Answer

When homologous chromosomes fail to separate in meiosis I, all four resulting gametes receive an abnormal number of chromosomes.

Question 5

In an enzyme-substrate interaction, what does the Michaelis constant (Km) represent?

Accepted Answer

Substrate concentration at half-maximal velocity

Answer

Km is the substrate concentration at which the reaction rate is half of Vmax, indicating the enzyme's affinity for its substrate.

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